The present invention relates to a method for extending the shelf life of juices, particularly citrus juice such as orange juice, without pasteurization, by subjecting the juice to an ultra high pressure homogenization step.
Homogenization of orange juice for the purpose of reducing the mean particle size of the pulp and for reducing the viscosity of orange juice concentrate is known in the art (see U.S. Pat. No. 4,946,702). Low viscosity orange juice concentrates are produced by a high shear treatment of concentrate in a high pressure homogenizer. In order to achieve a high shear treatment, commercial homogenizer pressures on the order of 3000 psi to a maximum of 8000 psi are commonly used. In such applications an APV Gaulin Corp. model 15MR homogenizer can be used. Such homogenizers can provide a maximum pressure of about 9500 psi to 10,000 psi.
In the most widely used type of homogenization process, the liquid material such as juice, concentrate or emulsion is introduced at pressures of from 500 psi to 10,000 psi into a central bore within an annular valve seat. (See FIG. 1). The liquid material is forced out through a narrow gap between the valve seat and a valve plate. Upon passing through the gap, the liquid material undergoes extremely rapid acceleration as well as an extreme drop in pressure. This violent action through the valve breaks down globules such as pulp or oils in the juice or the concentrate within the liquid material to produce the homogenized product.
The degree of homogenization is a function of the difference between the pressure of the liquid material at the inlet of the valve and the pressure at the outlet. Commercial homogenizers used for citrus juices have typically been operated at inlet pressures of no greater than 10,000 psi.
As known to those skilled in the art, single-strength orange juice refers to freshly extracted juice having a Brix of about 10.0-12.5. In order to extend the shelf life of single-strength citrus juice a pasteurization step is ordinarily conducted. For orange juice, heating at 185.degree. for 20 seconds is a typical pasteurization condition. However, it would be desirable to simplify processing and eliminate the pasteurization step if the same shelf stability or a commercially acceptable shelf stability could otherwise be achieved. From a practical point of view, there is a perception in the mind of the consumer that an unpasteurized juice is highly desirable and, hence, there may be a marketing advantage to a juice which is more stable than normal unpasteurized juice but has not been heat pasteurized.
It is, therefore, the object of the present invention to provide a method for processing single-strength juice, such as citrus juice, having an extended shelf life which does not require any pasteurization step.
It is a further object of the invention to provide a method for homogenizing orange juice and other juices, which effectively reduces the microbiological activity in the juice thereby contributing to an extension of its shelf life without pasteurization.